The processing of waste including municipal waste, medical waste, toxic and radioactive waste by means of plasma-torch based waste processing plants is well known. Referring to FIG. 1, a typical prior art plasma-based processing plant (1) comprises a processing chamber (10) typically in the form of a vertical shaft, in which typically solid, and also mixed (i.e., generally, solid plus liquid and/or semiliquid), waste (20) is introduced at the upper end thereof via a waste inlet means comprising an air lock arrangement (30). One or a plurality of plasma torches (40) at the lower end of the chamber (10) heats the column (35) of waste in the chamber (10), converting the waste into gases that are channeled off via outlet (50), and a liquid material (38) (typically molten metals and/or slag) which is periodically or continuously collected at the lower end of the chamber (10) via reservoir (60). Oxidising gases or fluids, such as air, oxygen or steam (70) may be provided at the lower end of the chamber (10) to convert char residues comprising carbon, produced in the processing of organic waste, into useful product gases such as CO and H2, for example. A similar arrangement for dealing with solid waste is described in U.S. Pat. No. 5,143,000, the contents of which are incorporated herein by reference thereto.
During operation of such a plant (1), products of the waste gasification are generated, including gases, liquid droplets and solid particles, which are removed from the chamber (10) by the outflow of product gases therefrom via outlet (50).
The product gases include gases such as for example hydrocarbons with general formula CnHm, and also CO, H2, N2, CO2, H2O, HC1, H2S, NH3, HF and other gases.
The liquid droplets may contain a variety of chemical compounds, and the physical form of the liquid may range from a tar-like substance to a light water soluble distillate.
The solid products may consist of small particles of waste (which are carried out by gas via outlet (50)) and of small particles of solid components which were formed as vapor in the lower (hotter) part of reactor or chamber (10), and then were condensed in the upper part of the chamber (10). These products may also include dioxins produced from the raw material in the waste. These solid particles which are carried out from the chamber (10) are typically known as “fly ash”. The greater the speed of the product gases leaving the chamber (10), the greater the amount of fly ash that is removed from the chamber (10). This fly ash generally comprises organic and inorganic compounds. Organic compounds may include, for example, components of paper, textile and other materials, which in turn may also comprise some proportion of inorganic materials too. For example, inorganic matter may constitute more than 20% of paper used in some paper products, the inorganic matter originating from the mineral fillers and coating pigments, including for example calcium carbonate, china clay and metal oxides, used to provide colour inks in the printing process. The inorganic compounds may also include different salts and metals, other than just oxides thereof, and may form part of raw waste material and/or may be formed during reactions at the lower part of chamber (10).
Typically, the product gases including the liquid and solid products entrained therewith are channeled off to a suitable post-processing means (2) comprised in the plant (1) and operatively connected to the chamber (10) via outlet (50), illustrated in FIGS. 2(a), 2(b), 3(a) and 3(b). The actual form of the post-processing means (2) will generally depend on the specific use of the plant (1) and its size/capacity.
For example, as illustrated in FIG. 2(a), in some large-scale plants (1), the post-processing means (2) may comprise an afterburner (3) and an energy generating system (4), followed by a gas cleaning system (5) and stack (6). The energy generating system (4) is adapted to produce (typically electrical) energy, which may be used to run the plant (1) and/or exported. As illustrated in FIG. 2(b), in smaller-scale plants (1), such as for example those used for the treatment of medical or other hazardous waste, may not provide sufficient product gases to justify an energy generating system, which is therefore replaced with a combustion products cooling system (9).
In the plants illustrated in FIG. 2(a) and FIG. 2(b), the gasification products generated in, and channeled off from, the chamber (10) are directed into the afterburner (3) wherein all organic materials (in gaseous, liquid or solid form) are combusted, forming CO2, H2O, N2, SOx, HCl, HF, P4O10, NOx and other combustion products, and wherein the inorganic materials form oxides and salts. Depending on the composition of the original waste, and if temperature in the afterburner (3) is not high enough and/or residence time of gases therein is small, dioxins may be formed. In order to eliminate dioxins, the combustion temperature needs to be higher than 850° C. (or higher than 1200° C. if the amount of chlorine in the waste is greater than about 1% by mass), and residence time in the afterburner (3) also needs to exceed 2 seconds. Under these minimal conditions, dioxins (that may exist in the gas products introduced into the afterburner (3)) will be oxidized, and thus destroyed.
While dioxins may exists in the waste materials before processing, in prior art apparatuses the major proportion of dioxins is formed during combustion of materials, including chlorine-containing organic materials, especially if the combustion temperature is low and the residence time in the afterburner is also low. Further, fly ash also tends to contain some metal compounds, especially copper-containing compounds which act as catalysts helping to form dioxins which are adsorbed in the fly ash, leading to high levels of toxicity in the fly ash formed with prior art apparatuses. In any case, even if the combustion temperature and residence time is sufficiently high to prevent the formation of dioxins in the afterburner, enough dioxins may still be formed during the cooling of combustion products in the boiler. This is particularly so if some of the organic materials in the waste were not fully combusted in the afterburner. To prevent this production of dioxins, it is necessary to have a high combustion temperature and to quench the products of combustion.
Alternatively, and as illustrated in FIG. 3(a) and FIG. 3(b), the post-processing means (2) may comprise a gas cleaning system (5′), for removing from the product gases leaving the chamber (10) toxic and corrosive components, such as for example HCl, HF, H2S and so on, and also including Cl, S, F and others, and also oils, tars, dust, carried with the product gases. The gas cleaning system (5′) is connected to a waste water treatment system (7), which also cools and cleans the water before recycling. The clean fuel gas leaving the gas cleaning system (5′), typically comprising CO, H2, N2, CO2, CH4 is channeled to a suitable energy generating system (4) operatively connected to a stack (6), as illustrated in FIG. 3(a). In the energy generating system (4), the fuel gases are combusted in a gas turbine arrangement, which is operatively connected to an electric generator, and typically also to an air compressor. Hot combustion products (at a temperature of about 450° C. to 550° C.) from the gas turbine are directed to a boiler where steam is produced for a steam turbine, which when coupled with an electric generator also generates electrical power. Such an electrical power generating scheme is known as a “combined cycle” and is highly efficient. Alternatively, and as illustrated in FIG. 3(b), the clean fuel gas may be sold to customers (8), for the cement plants, for example, or other uses. For the types of systems illustrated in FIGS. 3(a) and 3(b), chlorine is usually taken out of from the products in the cleaning system before they are directed to the combustion system or sold. Thus, dioxins are not generally formed in such systems.
Depending on the type of post-processing means (2) used in the plant (1), different residues are precipitated in the post-processing means (2), these residues being non-gaseous, and typically solids and/or liquids and/or mixtures thereof. Although the exact composition and physical form of these residues depends on the type of post-processing means (2) and on the composition of the waste processed by the chamber (10), these residues may be divided by any suitable categories, including for example, their physical state (powder, sludge or liquid, for example), by their chemical composition, by the size of particles, and so on. Herein, these residues are conveniently categorized into two types of residues, herein denoted Residues 1 (R1) and Residues 2 (R2), as defined hereinbelow.
Residues 1 (R1) may be defined as the residues that are formed only from the materials exiting from the chamber (10) via the gas outlet (50), and may include the products of their subsequent combustion in the post-processing means (2) (such as for example provided in the apparatuses illustrated in FIGS. 2(a) and 2(b)), and may further include products produced in a gas cleaning means such as a scrubber, for example, where only water (without additives) is used in the scrubber (such as for example provided in the apparatuses illustrated in FIGS. 3(a) and 3(b)).
Thus, Residues 1 (R1) may include mostly components of the treated waste and condensed vapors which are precipitated in the waste water treatment system (7) in the plants illustrated in FIGS. 3(a) and 3(b), that is, when only water without additives is used in first portion (7′) of the waste water treatment system (7). Such Residues (1) may include solid particles and tar (which is present in the products exiting the processing chamber), some water and some products formed from the reaction between some materials leaving the processing chamber and water. For example, the product gases may include hydrogen chloride gas, which may be diluted in the scrubber and form hydrochloric acid, which may then react with some solid particles and form salts, some of them soluble such as NaCl. Scrubber water may react with some components in the solid particles and may form hydroxides, and thus some of these salts and hydroxides may be recycled together with tars and other solids. In such cases, the Residues 1 (R1) may be in the form of a sludge, mixed with water from the waste water treatment system (7). Alternatively, the Residues 1 (R1) may include the materials forming after the oxidation in the afterburner (3), such as used in the plants illustrated in FIGS. 2(a) and 2(b), of the raw materials and condensed vapor carried out from the processing chamber. In such plants, some oxides and salts may be present in the raw material, i.e., the waste and additives which are fed to the processing chamber, and are then carried out of the chamber; some such materials may not be changed chemically in the afterburner. On the other hand, some materials may be changed chemically in the afterburner, for example metal to metal oxides, chlorides and so on, depending on the composition of the waste and conditions in the chamber and the afterburner.
Thus, Residues 1 (R1) are formed when the materials exiting the processing chamber via the gas outlet (50) are treated in the post-processing means (2) only with air (and/or oxygen) and/or by water, but without any additives. Thus, if additives or special reagents are used in the post-processing means (2), then Residues (2) are formed instead, as will be explained further hereinbelow.
Residues 2 (R2), on the other hand, while possibly also including Residues 1 (R1), are characterized in also including materials which originate from the input of additional substances into the post-processing means (2), in particular into the gas cleaning systems, and thus may include the actual additives and/or reagents used in the post-processing means (2), as well as the products of their reactions therein with materials carried from the processing chamber (10), and typically may be in the form of a sludge. Such Residues 2 (R2) may include, for the apparatuses illustrated in FIGS. 2(a) and 2(b), reagents such as Ca(OH)2, Na2CO3, NaOH, active carbon and others, which are used for binding acid gases (including, for example, SOx, HCl, HF, P4O10), and for trapping or adsorbing dioxins and heavy metal compounds. Products of reactions may include CaCl2, CaSO4, Ca3(PO4)2, CaF and/or NaCl, Na2SO4, Na3PO4, and others. Thus, Residues 2 (R2) may include some oxides and salts (which did not precipitate previously), reagents (since they are usually provided in amounts greater than required), and products of reaction. In the apparatuses illustrated in FIG. 3(a) and FIG. 3(b), part of the waste water is taken out from the first part (7′) of system (7), and is directed to the second part (7′) of the cleaning system (7) for special treatment by adding reagents, and by providing filtration and evaporation of solutions. In the second part (7″), Residues (2) are formed, and heavy metals may be transformed into solid hydroxides (for example, Cu(OH)2, Mn(OH)2, and others), and sulphides, including PbS, HgS and others. Chlorine may be transformed into dry NaCl.
Thus, in the afterburner (3) of FIG. 2(a), some dust (products of combustion) is precipitated as Residue 1 (R1). The products of combustion, including gases and dust, are directed to a boiler comprised in the energy generating system (4). Typically, steam is produced in the boiler, though at times hot water may be provided instead for customers, and the steam may be sold or may be used in steam turbine (with electric generator) for the generation of electricity. In the boiler some dust is precipitated too (i.e., as Residue 1 (R1)). Similarly, in the cooling system (9) of FIG. 2(b), some dust is also precipitated (i.e., as Residue 1 (R1)), which are also the products of combustion. In the plants illustrated in FIGS. 2(a) and 2(b), Residue 1 (R1) is typically in powder form.
Referring to FIG. 2(a), after the boiler in energy generating system (4), the products of combustion (including gases and dust) are directed to the gas cleaning system (5). Reagents, including for example Ca(OH)2, Na2CO3, NaOH, active carbon and/or other reagents, are used here for binding the acid gases, which may include SO2, HC1, HF, P4O10. Products of reaction between the reagents and the acid gases are formed, including, for example, CaCl2, CaSO4, Ca3(PO4)2, CaF and/or NaCl, Na2SO4, Na3PO4 and others. Hence, Residues 2 (R2) include some oxides and salts (which did not precipitate previously in the plant (1)), some quantity of reagents (since they are normally fed to the post-processing means (2) in amounts greater than the nominal proportions required), and products of reaction. Residue 2 (R2) may be in the form of a powder or sludge depending on the type of gas cleaning system (5) that is used.
For example, a “dry” gas cleaning system (5) suitable for the plant (1) illustrated in FIG. 2(a) may include a semi-dry scrubber, into which is fed a suspension of Ca(OH)2 in water for binding the acid gases. Water is subsequently evaporated fully, and thus only gases, products Ca(OH)2, CaCl2, CaSO4, Ca3(PO4)2, in powder form, and other dust (which did not precipitate in the boiler) exit the scrubber. After the scrubber there is a reactor-adsorber arrangement, wherein a mixture of powders of Ca(OH)2 and powdered activated carbon (PAC) are fed. These powdered adsorbants have very large specific surface values (typically carbon>750 m2/g; Ca(OH)2>30 m2/g), and the Ca(OH)2 may adsorb the remaining acid gases, while the PAC adsorbs dioxins and components containing heavy metals. After the reactor-adsorber there is a fabric filter arrangement where Residues 2 (R2) may be precipitated, including Ca(OH)2, active carbon, dioxins, some oxides and salts (which did not precipitate before), and products of reaction (CaC12, CaSO4, Ca3(PO4)2 and other substances). Essentially, gas carrying dust, which includes toxic components such as dioxins, heavy metals and their oxides and salts, is filtered through the layer of dust precipitated on the fabric of the bags and including adsorbents such as for example Ca(OH)2 and PAC, and the toxic components are adsorbed and thus precipitate out of the carrier gas. The clean gas obtained after filtration is directed to an exhauster and then to the stack (6) for expulsion into the atmosphere. Residues 2 (R2) obtained from such a cleaning system (in particular from the bag filter arrangement) do not include liquid, and thus such systems are known as “dry” cleaning systems. Residues 2 (R2) are very toxic and may include dioxins, compounds of heavy metals and Ca(OH)2, active carbon, some oxides and salts (which did not precipitate previously), products of reaction (such as, for example, CaCl2, CaSO4, Ca3(PO4)2 and other substances). However, since this Residue 2 (R2) is hygroscopic (especially the CaCl2 portion thereof), it may absorb water from the water vapour that is generated along with other combustion products, and thus may have a sludge-type consistency. Accordingly, in many instances tubes which are used for transporting this Residue 2 (R2) in the gas cleaning system (5) are heated to enable the Residue 2 (R2) to dry.
On the other hand, and referring to the post-processing means (2) illustrated in FIG. 2(b), atomized water, or water suspension with Ca(OH)2, or water solution of Na2CO3 or of NaOH may be used in the cooling system (9). When water is used, cooling system (9) acts only as a cooler, and Residues 1 (R1) are precipitated therein. When water with reagents is used (for binding the acid gases —SOx, HC1, HF, P4O10) the cooling system (9) also functions as a cooler, but additionally also forms simultaneously part of the cleaning system. In the latter case, Residues 2 (R2) are precipitated, and a reactor adsorber and bag filter arrangement may be provided, as described with respect to the arrangement of FIG. 2(a), mutatis mutandis.
Referring to the post-processing means (2) of the plants illustrated in FIG. 3(a) and FIG. 3(b), the gas cleaning system (5′) may comprise, for example, scrubbers and other means wherein the following materials are removed from the product gases: H2O, HCl, H2S, NH3, HF, oils, tars, dust and others. Waste water or waste aqueous solutions previously used in scrubber is transported to a waste water treatment system (7) for cooling and cleaning before being recycled to the gas cleaning system (5). Residues 1 (R1), comprising oils, tars and dust including fly ash, and even some reagents and products of reaction, are precipitated in a first portion (7′) of the waste water treatment system (7), and the recycled waste water is reintroduced into the gas cleaning system (5′). Part of waste water is taken out from the first part (7′) of the waste water treatment system (7) and is channeled to the second part (7″) thereof. This water contains an accumulation of components including heavy metals, chlorine compounds and others, and in the second part (7″) of the waste water recycling system (7″) heavy metals are transformed typically to solid hydroxides (such as, for example, Cu(OH)2, Mn(OH)2 and others) and to solid sulphides (such as, for example, PbS, HgS and others), and concurrently, Chlorine may be transformed in dry NaCl, for example. These solid residues are Residue 2 (R2).
Thus, in essence, such plasma-based processing plants of the art generate Residues 1 (R1) and Residues (R2), regardless of the specific details of the post-processing means (2), and a problem commonly encountered relating to the operation of such plasma-based processing plants (such as for example each one of the four prior art cases exemplified above) is the safe and economic disposal of the Residues 1 (R1) and Residues 2 (R2) obtained with the prior art post-processing means.
Particularly where the waste has a large proportion of heavy metals, dioxins and many other volatile materials (including some metals, metal oxides, chlorides, fluorides and others e.g., Cd, Hg, As, Zn, CdO, K2O, Na2O, CuO, CuCl, CdCl2, HgCl2, PbCl2, AsCl3, NiCl2, ZnCl2, MnCl2, and others) that have low boiling points and are thus vaporized in the chamber (10), these materials are entrained with the product gases, rather than being included in the slag. These volatile components will be eventually accumulated in the post-processing means (2), and particularly in the gas cleaning system, and can not be treated further in the prior art plants. As this can lead to unacceptable high levels of toxic components delivered to the stack (6), these residues must be removed for disposal, typically by land filling in the prior art.
In some prior art plants, the problem of disposal of Residues 1 (R1) is addressed by mixing the Residues 1 (R1) with water, drying this mixture and granulating the same. The granules are then fed to a separate specialized and dedicated plasma-based processing plant. However, this does little to solve the problem, since because of their composition and structure many granules are crushed during feeding and may be carried out by product gases again, or may be vaporized before reaching the hot zone of the plant, which thus results in a need for further, and possibly endless, recycling.
In another system (“The Plasma Treatment of Incinerator Ashes”, by D. M. Iddles, C. D. Chapman, A. J. Forde, C. P. Heanly, of Tetronics Ltd.) fly ash obtained from reciprocating grate incinerator and a fluidised bed was fed to an apparatus via the upper end of the apparatus. The apparatus is described as having a twin DC plasma arc heating system, such as to melt the feed. The apparatus produces a slag which may be a useful vitrified product, organic species are claimed to be destroyed, and gas treatment is required to deal with the gases produced. While such an apparatus may be an improvement over other prior art systems, the fly ash has to be separately transported and fed into the apparatus, adding cost and complexity to the conversion of the original municipal solid waste (MSW) or the sewage sludge waste (SSW). There is no suggestion that such an apparatus should be incorporated in a regular waste processing plant. Nevertheless, even if such a combination were formed, the apparatus would still add significant operating costs due to the plasma torches and so on. Further, in the apparatus disclosed, fly ash may still be entrained with product gases and removed from the processing chamber, and similarly volatile components in the fly ash are vaporized before reaching the hot zone, since the fly ash is introduced at the cooler end of the apparatus. Such prior art systems are also not suitable for dealing with Residues 2 (R2), in any case. The high temperatures of the apparatus destroys sulphates such as CaSO4 and Na2SO4 to SOx again. The SOx then needs to be bound again in a special gas cleaning system, where additional residues will be formed.
It is therefore an aim of the present invention to provide a system and method for dealing with non-gaseous residues produced in a waste converting plant, in particular plasma-torch based plants, which overcomes the limitations of prior art plants.
It is another aim of the present invention to provide such a system and method that may be incorporated into a municipal solid waste processing apparatus.
It is another aim of the present invention to provide such a system that is relatively simple mechanically and thus economic to incorporate into a processing plant design.
It is another aim of the present invention to provide such a system incorporated as an integral part of a plasma-torch based type waste converter.
It is also an aim of the present invention to provide such a system that is readily retrofittable with respect to at least some existing plasma-torch based waste converters.
The present invention achieves these and other aims by providing a system and method for redirecting non-gaseous residues, in particular Residues 1 and/or Residues 2, directly to the hotter parts of the processing chamber. In one embodiment this is accomplished by providing a reservoir for collecting residues precipitated by the post-processing means, and providing communication between the reservoir and the hotter part of the processing chamber by means of a direct connecting conduit. Means are then provided for transporting the residues into the chamber. In another embodiment, the residues are mixed with suitable additives, including slag produced by the processing chamber, and cementing adhesive or the like to form composite pellets or granules which are designed to be stable in the upper cooler part of the processing chamber. These pellets are then fed to the processing chamber via the top thereof with or without other regular waste. However, the majority of the residues inside the granules cannot be carried out by gases from the chamber or be chemically destroyed until the granules reach the high temperature regions of the chamber. Thereat, the residues inside the composite pellets are melted and/or possibly interact with slag and/or with additives inside the granules. So, part of the toxic components of residue will be destroyed, and part will be included in the molten slag, collected via a suitable reservoir. In other embodiments, both types of systems may be incorporated, and operated, separately or jointly.
The effect of introducing the residues into the high temperature zone of the processing chamber is to avoid some of the toxic compounds merely exiting the processing chamber relatively intact. Rather, some of the metal oxides which have low boiling points may interact with the slag and/or additives existing in the granules at the lower end of the processing chamber, forming solid solutions which have a much higher melting point than that of its components. In this way, at least some of the heavy metals (including for example Cd, Zn and Pb) may be included in the vitrified slag, and thus prevented from contaminating the environment either as part of the gases leaving the stack (6) or in by way of burial of residues in a landfill. Similarly, dioxins comprised in the residues, when introduced to the high temperature zone of the chamber (10), are reduced to HCl, CO and hydrocarbons, which are subsequently pyrolysed and oxidized in the gasification zone of the chamber (10) to generate CO.
It is important to note that the present invention comprises a waste processing chamber that is adapted to accommodate a column of waste and to enable the waste to migrate through the chamber in a downstream direction. The column of waste between the hot zone (that is provided by the plasma torches) and the gas outlet provides a tortuous matrix structure for gases that are formed in the gasification process, so that the escape of gases from the chamber is substantially retarded. This gives an opportunity for slag and other substances flowing downwards through the chamber to interact with residues being carried by the gases, as explained above, to the gas outlet. The position of the gas outlet in relation to the melting zone is thus also important in the context of the present invention. In the absence of a column of waste, or where the gas outlet is not upstream of the hot zone, the gases carrying the residues are substantially freely vented from the chamber, and cannot effectively interact with slag or other materials that are input to the processing chamber. Furthermore, the column of waste helps to maintain quasi steady state conditions within the processing plant, and a stable temperature profile is also maintained therein, comprising a relatively cooler upper zone, herein the gasification zone, where organic material is gasified, and a lower hotter zone, herein the melting zone, in which substantially all the inorganic materials are converted into molten metals and non-metallic inorganic slag, close to the plume generated by the plasma torches of the processing chamber. As inorganic waste in the downstream part of the column is melted, and as organic waste in the upper part is gasified, the waste in the column gradually migrates towards the downstream end, and more waste may be input into the chamber. This, however, does not substantially affect the quasi-steady state conditions referred to above. The conditions provided in the melting zone include sufficient temperature and residence time, such that the slag is sufficiently melted so that when it is removed from the chamber and subsequently cooled it forms solidified fused slag. However, the melting zone may also be adapted to be a vitrification zone, in which the conditions, i.e., temperature and/or residence time are increased sufficiently such that at least part of the slag is vitrified, and thus has a glassy, non-crystalline structure after solidification outside of the chamber.
CH 691507 relates to a method, and device, for burning solid or viscous material in grate firing unit. The method involves delivering material to a grate (2) and burning it. Hot gases are conducted through further units (9, 12, 15, 20), in which pollutants in the gases are at least partly separated out. The unburned material is conducted as slag to a slag remover (3). The pollutant residues are collected from the gases, which are preferably passed through a steam boiler (9) and a mixer (12) to remove pollutants, and the pollutants returned to the grate. This arrangement supposedly has advantages of high combustion efficiency with reduced residual waste and pollutant levels.
In the first place, this reference is concerned with the combustion of materials using a grate firing unit. This is very different from a high temperature (typically plasma-based) waste processing plant, in which the conditions include higher working temperatures and residence times such as to melt metals therein. Further, the pollutants of this reference are introduced between two portions of the grate, and it is unclear whether this is actually the high temperature zone provided by the combustion process therein. Furthermore, the grate arrangement, if used with plasma torches instead of a combustion system would result in molten slag being deposited onto the grate, which would thus become dogged and inoperative, and/or in the grate itself melting. In particular, the disclosed device of this reference is not adapted for accommodating a column of waste—rather, waste is fed onto the grate and burned thereon. Also, the gases are removed well downstream of the grate, and therefore cannot in any case interact with the waste or any other material that is being input to the chamber. Accordingly, the advantages of the present invention are not so readily achievable with the device and method of this reference. Finally, there is no disclosure at all of the pollutants being provided in the form of pellets via the waste inlet of the incinerator.
WO 89/09253 relates to a method and device for the incineration of refuse. Flyash produced by incineration in the plant (and optionally other sources) is introduced into the refuse being incinerated. In contrast to the present invention, though, the flyash is introduced at the cold upper part of the chute, at a location where the temperature is about 20° C., rather than in the hot kiln. Furthermore, the flyash is introduced as powder, or as a sludge, mixed with a liquid, and not in pellets of the type of the present invention. Hence, this reference neither discloses nor suggests the present invention. Moreover, the incinerator of the reference does not comprise a gas outlet upstream of the kiln, and if it were to be fitted with plasma torches and a gas outlet in the waste processing chamber, the flyash would continue to be ejected out therefrom via the gas outlet. In the reference, gas is passed from the downstream end of the kiln to an electrostatic filter via a baffle and boiler. This reference therefore does not disclose or suggest the present invention.
EP 324 454 relates to a method for cleaning the smoke gases from large combustion units, in which the largest part of the solid matter carried by the smoke gases (flue ash) is separated by dry dust filtering (9), the remaining solid matter is precipitated in a subsequent acid smoke gas scrubber (10) and wherein the solid matter in the dry dust filtering is melted down possibly together with waste and/or admixtures melting to glass and the solid matter elutriated in the smoke gas scrubbing is extracted and filtered. The method is directed to combustion units rather than to high temperature (plasma-torch) based processing plants. Further, there is no disclosure or suggestion of the combustion unit being adapted for accommodating a column of waste, or of the flyash being input into the high temperature zone of the combustion unit, or of forming the flyash into pellets for feeding into the top of the combustion unit together with waste, in contrast to the present invention. Even less so is there any suggestion of slag being recycled into the combustion unit.
U.S. 2002/006372 relates, inter alia, to a waste treatment equipment and method in which waste is passed from a low temperature horizontal type rotary drum furnace, to a high temperature combustion melting furnace, and water insoluble constituents k are returned to the low temperature furnace, while solid residues therefrom (not carried by gas) are fed into the high temperature melting furnace. Thus, this reference does not disclose a processing chamber as in the present invention—indeed the rotary furnace by definition cannot accommodate a column of waste—and the gas-borne residues are eventually input to the low temperature furnace, rather than the hotter melting furnace. There is also no disclosure or suggestion that the dust collected by dust collectors is to be directly input to the high temperature region of the melting furnace. Finally, there is no suggestion or disclosure of the residues being formed into pellets, or of these and/or slag being fed at the cooler end of the furnace in the manner of the present invention.
WO 99/23419 relates to an explosion-proof, closed reaction chamber for disposal of objects containing explosive material. The chamber has a vacuum aperture, through which after the reaction is completed gases and easily movable reaction products can be sucked away. The inner surface has a temperature-resistant lining with a protection against splinters. The feed device comprises a movable floor aperture. The floor is hydraulically driven. An ignition device comprising a gas flame activates desired rapid reactions. It can also comprise an electrical light arc. A shock and thrust absorber consists of a large metal body and a second absorber device for thrust loads is incorporated in the upper side of the chamber. The chamber itself is thus not adapted for accommodating a column of waste, nor are there any residues that are input into the chamber. Rather, gases are transferred from the chamber via the upper opening to a plasma chamber, and eventually, residues originating from the plasma chamber and from the reaction chamber are reintroduced to a sluice. Thus, in contrast to the present invention, the plasma chamber is not for processing waste, nor is it adapted for accommodating a column of waste, but rather only accepts gaseous products from the reaction chamber. Further, there is no suggestion of the residues being provided to the hot zone of the plasma chamber, but are instead provided to the sluice. There is absolutely no hint of the residues being formed into high temperature pellets, nor of these or the slag being reintroduced to the plasma chamber via the upper cooler end thereof, in contrast to the present invention.
FR 2691524 relates to the disposal of radioactive graphite without contaminating the environment, by pulverising, mixing with water and burning, then purifying combustion gases and recycling unburnt solids. Graphite pieces are crushed and powdered in two stages to less than 200 microns particle size, then mixed with water and emulsifying and wetting agents to form a suspension. This. suspension is pumped through a heater (E) to a two-stage burner and the resulting combustion gases are purified before release to the environment, by passing through cylone(s), gas-washing system and absolute filter. Solids recovered from stages and are recycled to mixer. Gases may be cooled in heat exchanger before the washing stage, to recover some combustion heat. Alternatively, the gases are cooled by finely sprayed water. In either case gases are reheated to 80° C. before the final filtration. Thus, this reference merely relates to residues being reintroduced into the burners together with the “waste”, in other words, there is no teaching at all of introducing the residues directly at the hot zone of the burners, or in the form of high temperature pellets with the waste.
DE 4333510 relates to a process for removing dust and toxic substances from hot gases. The process comprises introducing gases into a gas cooler, removing dust by a hot gas filter and passing through boiler and gas washer before release to the atmosphere. Hot dust-laden toxic gases arise from the combustion of liquid paste and solid residues in a rotating furnace and an afterburner chamber, and are then discharged to an assembly where they are treated. The hot gases are first introduced at 1200° C. into a gas cooler, where they cool to 800° C. before the dust is removed by a hot gas filter. The hot dust-free gases are then passed through a boiler where they surrender heat and generate steam. The hot gases are then passed through a gas washer before release to the atmosphere. The process removes substances from the gases which otherwise have a severe detrimental effect upon the system components through which they pass. Thus, this reference merely relates to dust residues being reintroduced into the rotating furnace together with the original waste, in other words, there is no teaching at all of introducing the residues at the hot zone of the furnace.